1. Field of the Invention
The invention generally relates to an image forming apparatus and a method for maintaining a head provided in the image forming apparatus. More specifically, the invention relates to an inkjet image type forming apparatus including a head that discharges a recording liquid such as ink to form images, and a method for maintaining the head in such an image forming apparatus.
2. Description of the Related Art
An inkjet image forming apparatus generally includes a head with micronozzles to spray droplets of a recording liquid. Such an inkjet image forming apparatus has various inkjet systems. For example, the image forming apparatus with a movable actuator inkjet system may be typically represented by piezoelectric inkjet printers and those with a film boiling inkjet system may be typically represented by thermal inkjet printers (e.g., Japanese Patent Application Publication No. 2004-268477 and Japanese Patent Application Publication No. 2007-168277).
In such image forming apparatuses, recording heads are generally provided with corresponding caps. These caps are attached to the respective heads to avoid nozzle clogging and/or reduction of the recording liquid due to dryness while the heads are not driven (e.g., Japanese Patent Application Publication No. 2004-268477). However, simply providing the caps on the heads while the heads are not driven may not completely prevent the clogging of the nozzles and the reduction of the recording liquid due to dryness. Other technical proposals have been disclosed to improve liquid jet performance of the nozzles. Examples of such techniques of nozzle maintenance are disclosed in Japanese Patent Application Publication No. 2004-268477 and Japanese Patent Application Publication No. 2007-168277. According to these nozzle maintenance techniques, the recording liquid is discharged into the caps provided for the heads, or the recording liquid is forcefully discharged while images are not formed (these types of recording liquid discharge may hereinafter be called “non-image forming discharge”).
Japanese Patent Application Publication No. 2007-168277 discloses an example of an image forming apparatus to which such nozzle maintenance techniques are applied. The disclosed image forming apparatus includes an endless belt to transfer a recording medium such as paper to a counterpart region facing the heads, where the recording liquid is discharged via holes provided in the endless belt without transferring the paper.
However, with such a configuration, where the recording liquid is discharged via the holes in the endless belt, the endless belt may be contaminated or it may take a long time to complete the non-image forming discharge. That is, part of recording liquid droplets may be attached to a surface of the endless belt without passing through its holes while conducting the non-image forming discharge. In such a case, recording media (e.g., paper) subsequently transferred by the endless belt may be contaminated or other components arranged inside the image forming apparatus may be contaminated while images are formed on the recording media. However, if the amount of recording liquid for the non-image forming discharge is simply reduced per hour to avoid such contamination of the endless belt and other components with the recording liquid, it may take a long time to complete the non-image forming discharge. In addition, since the endless belt is provided with the holes, airflow disturbance near the belt surface may be caused by the belt travelling speed. Thus, recording liquid jetting directions may be misaligned, which may also contaminate the belt surface.